How to Determine the Amount of Phosphorus for Grass

Don't apply phosphorus unless you know the soil requires it.

Phosphorus has become a dirty word among the environmentally conscious. Although it's a nutrient that all life requires, excess phosphorus -- that which runs off our lawns and into the waterways -- wreaks havoc with the flora and upsets the balance of nature. Healthy turfgrass blades contain a 0.3 percent phosphorus concentration, according to scientists with the State Environmental Resource Center. Before applying fertilizer to the lawn, take the time to determine how much phosphorus it truly needs. Phosphorus is represented by the middle number on the fertilizer bag.

Things You'll Need

• Knife
• Garden trowel
• Bucket

Instructions

1. Scrape the grass off a small patch of lawn. Use a garden trowel to dig down 3 inches and remove some soil. Repeat this procedure in five random areas around the lawn.

2. Mix the soil samples in a bucket. The cooperative extension office will advise you as to how much of this combined sample to send. Some offices provide bags or boxes for mailing the samples.

3. Wait for the soil test results from the extension. The results will let you know how much phosphorus to apply to the lawn.

Tips & Warnings

• Allow lawn clippings to remain on the lawn after mowing. The ejected grass from the lawnmower contains .13 pounds of phosphorus per 1,000 square feet, according to the State Environmental Resource Center. This makes them a good source of natural fertilizers.

• It is illegal in several states to apply fertilizers containing phosphorus to lawns. Check with your county cooperative extension office to determine if your state is among them.

References

• State Environmental Resource Center; Phosphorus Pollution; January 2005
• University of Minnesota: How to Sample -- Homeowners
• University of Vermont Extension; Does Your Lawn Really Need Phosphorus?; Sid Bosworth, et al.

Resources

• U.S. Highbush Blueberry Council: Cooperative Extensions